US 20070024824 A1 Abstract A method of displaying an image with a display system includes receiving image data for the image. The method includes generating a first sub-frame and a second sub-frame corresponding to the image data. The method includes projecting the first sub-frame onto a target surface using a first projector light source. The method includes projecting the second sub-frame onto the target surface using a second projector light source, wherein the first and the second sub-frames at least partially overlap on the target surface, and wherein the first and the second light sources have substantially different spectral distributions.
Claims(29) 1. A method of displaying an image with a display system, the method comprising:
receiving image data for the image; generating a first sub-frame and a second sub-frame corresponding to the image data; projecting the first sub-frame onto a target surface using a first projector light source; and projecting the second sub-frame onto the target surface using a second projector light source, wherein the first and the second sub-frames at least partially overlap on the target surface, and wherein the first and the second light sources have substantially different spectral distributions. 2. The method of 3. The method of 4. The method of providing a first color filter associated with the first light source and configured to pass a first color of light from the first light source and block other colors of light from the first light source; and providing a second color filter associated with the second light source and configured to pass a second color of light from the second light source and block other colors of light from the second light source. 5. The method of 6. The method of generating a third sub-frame corresponding to the image data; and projecting the third sub-frame onto the target surface using a third projector light source, wherein the first, the second, and the third sub-frames at least partially overlap on the target surface, and wherein the first, the second, and the third light sources have substantially different spectral distributions. 7. The method of 8. The method of 9. The method of 10. The method of 11. The method of generating a fourth sub-frame corresponding to the image data; projecting the fourth sub-frame onto the target surface using a fourth projector light source; and wherein the first, the second, the third, and the fourth sub-frames at least partially overlap on the target surface, and wherein the first, the second, the third, and the fourth light sources have substantially different spectral distributions. 12. The method of 13. A system for displaying an image, the system comprising:
a buffer adapted to receive image data for the image; a sub-frame generator configured to define first and second sub-frames corresponding to the image data; a first projection device adapted to project the first sub-frame onto a target surface using a first light source; and a second projection device adapted to project the second sub-frame onto the target surface using a second light source with substantially different spectral characteristics than the first light source, wherein the second sub-frame at least partially overlaps the first sub-frame. 14. The system of 15. The system of 16. The system of a first color filter associated with the first light source and configured to pass a first color of light from the first light source and block other colors of light from the first light source; and a second color filter associated with the second light source and configured to pass a second color of light from the second light source and block other colors of light from the second light source. 17. The system of 18. The system of a third projection device adapted to project the third sub-frame onto a target surface using a third light source with substantially different spectral characteristics than the first and second light sources. 19. The system of 20. The system of 21. The system of 22. The system of 23. The system of a fourth projection device adapted to project the fourth sub-frame onto a target surface using a fourth light source with substantially different spectral characteristics than the first, second, and third light sources. 24. The system of 25. A system for projecting low-resolution sub-frames onto a viewing surface at spatially offset positions to generate the appearance of a high-resolution image, the system comprising:
means for receiving a first high-resolution image; means for generating a first plurality of low-resolution sub-frames based on the first high-resolution image; first means for generating a first color of light for projecting a first one of the sub-frames; second means for generating a second color of light for projecting a second one of the sub-frames; and wherein the first means generates more energy for the first color of light than the second means, and the second means generates more energy for the second color of light than the first means. 26. The system of third means for generating a third color of light for projecting a third one of the sub-frames; and wherein the third means generates more energy for the third color of light than the first and second means. 27. The system of 28. The system of fourth means for generating a fourth color of light for projecting a fourth one of the sub-frames; and wherein the fourth means generates more energy for the fourth color of light than the first, second, and third means. 29. The system of Description This application is related to U.S. patent application Ser. No. 11/080,223, filed Mar. 15, 2005, and entitled PROJECTION OF OVERLAPPING SINGLE COLOR SUB-FRAMES ONTO A SURFACE and U.S. patent application Ser. No. 11/080,583, filed Mar. 15, 2005, and entitled PROJECTION OF OVERLAPPING SUB-FRAMES ONTO A SURFACE, both of which are hereby incorporated by reference herein. Two types of projection display systems are digital light processor (DLP) systems, and liquid crystal display (LCD) systems. It is desirable in some projection applications to provide a high lumen level output, but it is very costly to provide such output levels in existing DLP and LCD projection systems. Three choices exist for applications where high lumen levels are desired: (1) high-output projectors; (2) tiled, low-output projectors; and (3) superimposed, low-output projectors. When information requirements are modest, a single high-output projector is typically employed. This approach dominates digital cinema today, and the images typically have a nice appearance. High-output projectors have the lowest lumen value (i.e., lumens per dollar). The lumen value of high output projectors is less than half of that found in low-end projectors. If the high output projector fails, the screen goes black. Also, parts and service are available for high output projectors only via a specialized niche market. Tiled projection can deliver very high resolution, but it is difficult to hide the seams separating tiles, and output is often reduced to produce uniform tiles. Tiled projection can deliver the most pixels of information. For applications where large pixel counts are desired, such as command and control, tiled projection is a common choice. Registration, color, and brightness must be carefully controlled in tiled projection. Matching color and brightness is accomplished by attenuating output, which costs lumens. If a single projector fails in a tiled projection system, the composite image is ruined. Superimposed projection provides excellent fault tolerance and full brightness utilization, but resolution is typically compromised. Algorithms that seek to enhance resolution by offsetting multiple projection elements have been previously proposed. These methods assume simple shift offsets between projectors, use frequency domain analyses, and rely on heuristic methods to compute component sub-frames. The proposed systems do not generate optimal sub-frames in real-time, and do not take into account arbitrary relative geometric distortion between the component projectors, and do not project single-color sub-frames. Existing projection systems do not provide a cost effective solution for high lumen level (e.g., greater than about 10,000 lumens) applications. Conventional projectors typically use a single light source and red, green, and blue light filters to produce multi-color images. In some conventional projectors, the red, green, and blue light filters are positioned on a color wheel. The color wheel is rotated to sequentially produce red, green, and blue (RGB) light. The red, green, and blue light is temporally multiplexed, so only one color is projected at a time. This temporal multiplexing can cause sequential color artifacts. In addition, a blanking period is typically provided between colors so that one color does not blend into the next, and light is wasted during these periods. Single light source projection systems typically use a light source with a broad spectrum so that enough energy in RGB is obtained when used with RGB color wheels or color filters. The single light source systems with broad spectrum coverage are typically sub-optimal or expensive. Typically, Xenon lamps have such a broad spectral characteristic but are expensive and subject to explosions. Many ultra-high pressure (UHP) light sources, such as Metal-Halide lamps and Mercury arc lamps, also provide broad spectrum coverage, but have a “peaky response”. Having to design lamps for broad spectrum makes them either too costly or significantly sub-optimal for a particular color. Further, there may be regions in the lamp spectrum that fall between the responses of two color channels and that are wasted (filtered out by the RGB filters, and not used). The natural spikes in the lamp response are often wasted in order to preserve the purity of color primaries, or may be included in red, green, or blue, thereby producing “dirty colors”. Multi-lamp systems have been used in the past, but these prior systems are not aimed at overall color and efficiency optimization, but instead target overall brightness gain. One form of the present invention provides a method of displaying an image with a display system. The method includes receiving image data for the image. The method includes generating a first sub-frame and a second sub-frame corresponding to the image data. The method includes projecting the first sub-frame onto a target surface using a first projector light source. The method includes projecting the second sub-frame onto the target surface using a second projector light source, wherein the first and the second sub-frames at least partially overlap on the target surface, and wherein the first and the second light sources have substantially different spectral distributions. In the following Detailed Description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology, such as “top,” “bottom,” “front,” “back,” etc., may be used with reference to the orientation of the Figure(s) being described. Because components of embodiments of the present invention can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following Detailed Description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims. In one embodiment, image display system Image frame buffer Sub-frame generator In one embodiment, sub-frames Projectors A problem of sub-frame generation, which is addressed by embodiments of the present invention, is to determine appropriate values for the sub-frames It will be understood by a person of ordinary skill in the art that functions performed by sub-frame generator Also shown in In one embodiment, display system In one form of the invention, image display system In one embodiment, display system In one embodiment, as illustrated in As illustrated in In one form of the invention, sub-frames In one form of the invention, display system In one embodiment, sub-frame generator One form of the present invention determines and generates single-color sub-frames where: -
- k=index for identifying individual sub-frames
**110**; - i=index for identifying color planes;
- Z
_{ik}=kth low-resolution sub-frame**110**in the ith color plane on a hypothetical high-resolution grid; - H
_{i}=Interpolating filter for low-resolution sub-frames**110**in the ith color plane; - D
_{i}^{T}=up-sampling matrix for sub-frames**110**in the ith color plane; and - Y
_{ik}=kth low-resolution sub-frame**110**in the ith color plane.
- k=index for identifying individual sub-frames
The low-resolution sub-frame pixel data (Y In one embodiment, F In one embodiment, the geometric mapping (F In another embodiment of the invention, the forward geometric mapping or warp (F A superposition/summation of such warped images where: -
- k=index for identifying individual sub-frames
**110**; - i=index for identifying color planes;
- X-hat
_{i}=hypothetical or simulated high-resolution image for the ith color plane in the reference projector frame buffer**120**; - F
_{ik}=operator that maps the kth low-resolution sub-frame**110**in the ith color plane on a hypothetical high-resolution grid to the reference projector frame buffer**120**; and - Z
_{ik}=kth low-resolution sub-frame**110**in the ith color plane on a hypothetical high-resolution grid, as defined in Equation I.
- k=index for identifying individual sub-frames
A hypothetical or simulated image where: -
- X-hat=hypothetical or simulated high-resolution image in the reference projector frame buffer
**120**; - X-hat
_{1}=hypothetical or simulated high-resolution image for the first color plane in the reference projector frame buffer**120**, as defined in Equation II; - X-hat
_{2}=hypothetical or simulated high-resolution image for the second color plane in the reference projector frame buffer**120**, as defined in Equation II; - X-hat
_{N}=hypothetical or simulated high-resolution image for the Nth color plane in the reference projector frame buffer**120**, as defined in Equation II; and - N=number of color planes.
- X-hat=hypothetical or simulated high-resolution image in the reference projector frame buffer
If the simulated high-resolution image In one embodiment, the deviation of the simulated high-resolution image where: -
- X=desired high-resolution frame
**308**; - X-hat=hypothetical or simulated high-resolution frame
**306**in the reference projector frame buffer**120**; and - η=error or noise term.
- X=desired high-resolution frame
As shown in Equation IV, the desired high-resolution image The solution for the optimal sub-frame data (Y where: -
- k=index for identifying individual sub-frames
**110**; - i=index for identifying color planes;
- Y
_{ik}*=optimum low-resolution sub-frame data for the kth sub-frame**110**in the ith color plane; - Y
_{ik}=kth low-resolution sub-frame**110**in the ith color plane; - X-hat=hypothetical or simulated high-resolution frame
**306**in the reference projector frame buffer**120**, as defined in Equation III; - X=desired high-resolution frame
**308**; and - P(X-hat|X)=probability of X-hat given X.
- k=index for identifying individual sub-frames
Thus, as indicated by Equation V, the goal of the optimization is to determine the sub-frame values (Y Using Bayes rule, the probability P(X-hat|X) in Equation V can be written as shown in the following Equation VI:
where: -
- X-hat=hypothetical or simulated high-resolution frame
**306**in the reference projector frame buffer**120**, as defined in Equation III; - X=desired high-resolution frame
**308**; - P(X-hat|X)=probability of X-hat given X;
- P(X|X-hat)=probability of X given X-hat;
- P(X-hat)=prior probability of X-hat; and
- P(X)=prior probability of X.
- X-hat=hypothetical or simulated high-resolution frame
The term P(X) in Equation VI is a known constant. If X-hat is given, then, referring to Equation IV, X depends only on the noise term, η, which is Gaussian. Thus, the term P(X|X-hat) in Equation VI will have a Gaussian form as shown in the following Equation VII:
where: -
- X-hat=hypothetical or simulated high-resolution frame
**306**in the reference projector frame buffer**120**, as defined in Equation III; - X=desired high-resolution frame
**308**; - P(X|X-hat)=probability of X given X-hat;
- C=normalization constant;
- i=index for identifying color planes;
- X
_{i}=ith color plane of the desired high-resolution frame**308**; - X-hat
_{i}=hypothetical or simulated high-resolution image for the ith color plane in the reference projector frame buffer**120**, as defined in Equation II; and - σ
_{i}=variance of the noise term, η, for the ith color plane.
- X-hat=hypothetical or simulated high-resolution frame
To provide a solution that is robust to minor calibration errors and noise, a “smoothness” requirement is imposed on X-hat. In other words, it is assumed that good simulated images where: -
- P(X-hat)=prior probability of X-hat;
- α and β=smoothing constants;
- Z(α, β)=normalization function;
- ∇=gradient operator; and
- C-hat
_{1}=first chrominance channel of X-hat; - C-hat
_{2}=second chrominance channel of X-hat; and - L-hat=luminance of X-hat.
In another embodiment of the invention, the smoothness requirement is based on a prior Laplacian model, and is expressed in terms of a probability distribution for X-hat given by the following Equation IX:
where: -
- P(X-hat)=prior probability of X-hat;
- α and β=smoothing constants;
- Z(α, β)=normalization function;
- ∇=gradient operator; and
- C-hat
_{1}=first chrominance channel of X-hat; - C-hat
_{2}=second chrominance channel of X-hat; and - L-hat=luminance of X-hat.
The following discussion assumes that the probability distribution given in Equation VIII, rather than Equation IX, is being used. As will be understood by persons of ordinary skill in the art, a similar procedure would be followed if Equation IX were used. Inserting the probability distributions from Equations VII and VIII into Equation VI, and inserting the result into Equation V, results in a maximization problem involving the product of two probability distributions (note that the probability P(X) is a known constant and goes away in the calculation). By taking the negative logarithm, the exponents go away, the product of the two probability distributions becomes a sum of two probability distributions, and the maximization problem given in Equation V is transformed into a function minimization problem, as shown in the following Equation X:
where: -
- k=index for identifying individual sub-frames
**110**; - i=index for identifying color planes;
- Y
_{ik}*=optimum low-resolution sub-frame data for the kth sub-frame**110**in the ith color plane; - Y
_{ik}=kth low-resolution sub-frame**110**in the ith color plane; - N=number of color planes;
- X
_{i}=ith color plane of the desired high-resolution frame**308**; - X-hat
_{i}=hypothetical or simulated high-resolution image for the ith color plane in the reference projector frame buffer**120**, as defined in Equation II; - α and β=smoothing constants;
- ∇=gradient operator;
- T
_{C1i}=ith element in the second row in a color transformation matrix, T, for transforming the first chrominance channel of X-hat; - T
_{C2i}=ith element in the third row in a color transformation matrix, T, for transforming the second chrominance channel of X-hat; and - T
_{Li}=ith element in the first row in a color transformation matrix, T, for transforming the luminance of X-hat.
- k=index for identifying individual sub-frames
The function minimization problem given in Equation X is solved by substituting the definition of X-hat where: -
- k=index for identifying individual sub-frames
**110**; - i and j=indices for identifying color planes;
- n=index for identifying iterations;
- Y
_{ik}^{(n+1)}=kth low-resolution sub-frame**110**in the ith color plane for iteration number n+1; - Y
_{ik}^{(n)}=kth low-resolution sub-frame**110**in the ith color plane for iteration number n; - Θ=momentum parameter indicating the fraction of error to be incorporated at each iteration;
- D
_{i}=down-sampling matrix for the ith color plane; - H
_{i}^{T}=Transpose of interpolating filter, H_{i}, from Equation I (in the image domain, H_{i}^{T }is a flipped version of H_{i}); - F
_{ik}^{T}=Transpose of operator, F_{ik}, from Equation II (in the image domain, F_{ik}^{T }is the inverse of the warp denoted by F_{ik}); - X-hat
_{i}^{(n)}=hypothetical or simulated high-resolution image for the ith color plane in the reference projector frame buffer**120**, as defined in Equation II, for iteration number n; - X
_{i}=ith color plane of the desired high-resolution frame**308**; - α and β=smoothing constants;
- ∇
^{2}=Laplacian operator; - T
_{C1i}=ith element in the second row in a color transformation matrix, T, for transforming the first chrominance channel of X-hat; - T
_{C2i}=ith element in the third row in a color transformation matrix, T, for transforming the second chrominance channel of X-hat; - T
_{Li}=ith element in the first row in a color transformation matrix, T, for transforming the luminance of X-hat; - X-hat
_{j}^{(n)}=hypothetical or simulated high-resolution image for the jth color plane in the reference projector frame buffer**120**, as defined in Equation II, for iteration number n; - T
_{C1j}=jth element in the second row in a color transformation matrix, T, for transforming the first chrominance channel of X-hat; - T
_{C2j}=jth element in the third row in a color transformation matrix, T, for transforming the second chrominance channel of X-hat; - T
_{Lj}=jth element in the first row in a color transformation matrix, T, for transforming the luminance of X-hat; and - N=number of color planes.
- k=index for identifying individual sub-frames
Equation XI may be intuitively understood as an iterative process of computing an error in the reference projector To begin the iterative algorithm defined in Equation XI, an initial guess, Y -
- where:
- k=index for identifying individual sub-frames
**110**; - i=index for identifying color planes;
- Y
_{ik}^{(0)}=initial guess at the sub-frame data for the kth sub-frame**110**for the ith color plane; - D
_{i}=down-sampling matrix for the ith color plane; - B
_{i}=interpolation filter for the ith color plane; - F
_{ik}^{T}=Transpose of operator, F_{ik}, from Equation II (in the image domain, F_{ik}^{T }is the inverse of the warp denoted by F_{ik}); and - X
_{i}=ith color plane of the desired high-resolution frame**308**.
Thus, as indicated by Equation XII, the initial guess (Y In another form of the invention, the initial guess, Y where: -
- k=index for identifying individual sub-frames
**110**; - i=index for identifying color planes;
- Y
_{ik}^{(0)}=initial guess at the sub-frame data for the kth sub-frame**110**for the ith color plane; - D
_{i}=down-sampling matrix for the ith color plane; - F
_{ik}^{T}=Transpose of operator, F_{ik}, from Equation II (in the image domain, F_{ik}^{T }is the inverse of the warp denoted by F_{ik}); and - X
_{i}=ith color plane of the desired high-resolution frame**308**.
- k=index for identifying individual sub-frames
Equation XIII is the same as Equation XII, except that the interpolation filter (B Several techniques are available to determine the geometric mapping (F where: -
- F
_{2}=operator that maps a low-resolution sub-frame**110**of the second projector**112**B to the first (reference) projector**112**A; - T
_{1}=geometric mapping between the first projector**112**A and the camera**122**; and - T
_{2}=geometric mapping between the second projector**112**B and the camera**122**.
- F
In one embodiment, the geometric mappings (F In one embodiment, the position of displayed sub-frames In one form of the present invention, each projector Curve In one form of the present invention, each of the light sources In one form of the invention, light sources In one form of the invention, light sources In another embodiment, light sources In one form of the invention, at least one of the light sources In one embodiment, projectors One form of the present invention is an image display system One form of the present invention provides an image display system In some existing display systems, multiple low-resolution images are displayed with temporal and sub-pixel spatial offsets to enhance resolution. There are some important differences between these existing systems and embodiments of the present invention. For example, in one embodiment of the present invention, there is no need for circuitry to offset the projected sub-frames It can be difficult to accurately align projectors into a desired configuration. In one embodiment of the invention, regardless of what the particular projector configuration is, even if it is not an optimal alignment, sub-frame generator Algorithms that seek to enhance resolution by offsetting multiple projection elements have been previously proposed. These methods assume simple shift offsets between projectors, use frequency domain analyses, and rely on heuristic methods to compute component sub-frames. In contrast, one form of the present invention utilizes an optimal real-time sub-frame generation algorithm that explicitly accounts for arbitrary relative geometric distortion (not limited to homographies) between the component projectors One form of the present invention provides a system Using multiple off the shelf projectors Image display system In one embodiment, image display system Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof. Referenced by
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